1. Field of the Invention
This invention relates to a seal for the space between an adjacent nuclear reactor vessel annular flange and a surrounding ledge or plate to provide a water barrier for supporting a liquid in a cavity called a refueling pool and, more particularly, to a permanent seal joint which is able to accommodate the radial, axial and rotational movements between the reactor vessel and the pool walls.
2. Description of Prior Art
A nuclear reactor vessel is typically positioned in a cavity or containment system. The reactor vessel is spaced from the cavity wall so as to provide an annular expansion gap and permit the reactor vessel to expand each in both a horizontal and vertical direction during cyclic heating and cooling periods of the reactor. An upper annular portion of the cavity above the vessel serves as a refueling canal or pool. The refueling pool, while maintained dry during reactor operation, is filled with water during refueling of the nuclear reactor. During refueling, the head of the reactor pressure vessel is removed and the refueling pool is filled with water.
The reactor pressure vessel has flanges which secure the head assembly to the body of the vessel. The cavity wall typically also has an edge or flange. During refueling operations, the annular gap between the reactor vessel and the pool floor must be closed tightly to prevent refueling water from entering the lower part of the reactor cavity. The seal between the reactor pressure vessel flange and the cavity wall flange serves as a floor for the body of water that is placed in the refueling pool.
Typically, this gap has been sealed using the contact seal or the gasket seal method by pressing a relatively soft material, the gasket, between the fluid passing surfaces to achieve a seal. These elastomeric seals, however, are subject to degradation and leakage. In addition, the gasket seal requires constant inspection and maintenance, which is difficult to perform in the gaskets' high dose radioactive and thermal environment and in view of the usually tight refueling schedules.
It is desirable, therefore, to provide a permanent seal which overcomes the disadvantages of the gasket seal. Attempts have been made to provide permanent seals, such as the seals described in U.S. Pat. No. 5,102,612, incorporated herein by reference and U.S. Pat. No. 4,904,442. The seal described in U.S. Pat. Nos. 4,904,442 and 5,102,612 are some type of vertically extending, straight walled inner and outer seal provided on an annular ring seal. These seals, however, are subject to high stresses and do not last as long as the life of the plant. These seals fail to accommodate the radial, axial and rotational movements between the reactor vessel and the pool floor for the life of the plant and fail to withstand the required heating and cooling cycles of the plants.
Thus it is a problem in the prior art to provide a permanent seal between the reactor vessel and pool floor which requires no maintenance or inspections, which can withstand the heating and cooling cycles of the plant, which can accommodate the radial, axial and rotational movements, between the reactor vessel and the pool floor for the life of the plant and which is not subject to leakage.